Testing automated sensor traps for mammal field studies

Abstract

Context Live traps are regularly used in field and enclosure studies with mammals. In some scenarios, such as, for example, when the focus is on temporal patterns or to minimise the time animals are contained inside the trap for animal-ethics reasons, it can be highly useful to be alerted immediately when an individual is trapped. Aims In the present study, an automated system was trialed that is designed to automatically send a signal to a receiving device (pager, computer, mobile phone) when the body heat or movement of a trapped small mammal is registered by an infrared sensor (ERMINEA permanent monitoring system for rodent detection). Methods Sensors were attached to Ugglan multiple-capture traps and used in laboratory conditions and in semi-natural outdoor enclosures with common voles (Microtus arvalis) and bank voles (Myodes glareolus), as well as in the field with bank voles, Apodemus species and common voles. Sensor readings were compared to visual observation and trapping results. Key results In enclosure and field conditions, 100% and 98.7% of traps recorded captured animals correctly. There were no sensor signals when rodents moved along the outside or in the entrance compartment of the traps. Rodents sitting on the trap door triggered the sensor in 50% of cases when there was no bedding in the trap; however, there were no sensor signals if bedding was present. In laboratory trials, 20–70% of traps were falsely triggered by large insects (crickets), depending on ambient temperature and whether bedding was in the trap. Conclusions Generally, the system was a reliable, flexible and easy-to-handle tool to monitor live captures. To minimise false negatives (animals trapped without signal), testing sensor function in the pre-baiting phase and software adjustments are recommended. Implications The sensors are compatible with various trapping and other monitoring devices, providing the potential to be used in a wide range of applications. Their use is likely to optimise study designs, especially when temporal patterns are recorded or animals or samples need to be obtained soon after capture, and to minimise stress of trapped animals because they can be removed shortly after capture.